<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button id="btn" message="我爱你">按钮</button>
  <script>
    const el = document.getElementById('btn'); // 获取到当前元素
    
    // 获取已存在的自定义属性
    console.log( el.getAttribute('message') );
    // 设置自定义属性
    el.setAttribute('name', '高圆圆');

    console.log('el -> ', el);
  </script>
</body>
</html>